Quantized conductance of a suspended graphene nanoconstriction

TL;DR

This paper reports the first observation of quantized conductance in a suspended graphene nanoconstriction at zero magnetic field, revealing quantum ballistic transport and effects like the 0.7 anomaly, advancing graphene quantum electronics.

Contribution

It demonstrates quantized conductance in suspended graphene nanostructures at zero magnetic field, highlighting quantum effects and electron interactions in high mobility graphene.

Findings

Quantized conductance at integer multiples of 2e^2/h observed

Transition to quantum Hall effect at magnetic fields above 60mT

Energy spacing of 8 meV between subbands

Abstract

A yet unexplored area in graphene electronics is the field of quantum ballistic transport through graphene nanostructures. Recent developments in the preparation of high mobility graphene are expected to lead to the experimental verification and/or discovery of many new quantum mechanical effects in this field. Examples are effects due to specific graphene edges, such as spin polarization at zigzag edges of a graphene nanoribbon and the use of the valley degree of freedom in the field of graphene valleytronics8. As a first step in this direction we present the observation of quantized conductance at integer multiples of 2e^2/h at zero magnetic field and 4.2 K temperature in a high mobility suspended graphene ballistic nanoconstriction. This quantization evolves into the typical quantum Hall effect for graphene at magnetic fields above 60mT. Voltage bias spectroscopy reveals an energy spacing of 8 meV between the first two subbands. A pronounced feature at 0.6 2e^2/h present at a magnetic field as low as ~0.2T resembles the "0.7 anomaly" observed in quantum point contacts in a GaAs-AlGaAs two dimensional electron gas, having a possible origin in electron-electron interactions.